Thermosensitive recording media are ordinarily prepared by mixing together a leuco dye and a color developing agent, such as a phenolic compound and the like, after grinding them into fine particles, preparing a coating solution by adding a binder, a filler, a sensitizer, a slipping agent and other aids to the mixture and applying the coating solution onto a substrate such as paper, synthetic paper, film, plastic and the like. Thermosensitive recording medium develops color through an instantaneous chemical reaction when heated by a thermal head, hot stamp, hot pen, laser light or the like to yield a recorded image. Such thermosensitive recording media are used extensively in recording media such as facsimile devices, computer terminal printers, automatic ticket dispensers, recorders for meters, receipts at super markets and convenience stores and the like.
In recent years, the use of the thermosensitive recording medium is expanding, such as various ticket, receipts, labels, ATM of Bank, meter reading of gas and electricity, cash vouchers, such as car racing or horseracing betting. Then thermosensitive recording medium has been required to have a good preservation property of an image portion and a blank portion under severe environment such as high temperature condition like in a car in mid-summer.
It is generally known to install a protective layer on the thermosensitive recording layer to improve the preservation property of the image portion of the thermosensitive recording medium.
However, when installing a protective layer on a thermosensitive recording layer, the protective layer absorbs the thermal energy given from the thermal head, so that the color developing property, that is color developing sensitivity and image quality, especially bar code readability, are deteriorated. In particular, when the color developing sensitivity is deteriorated and then the density difference between the recorded portion and the blank portion becomes smaller, and the barcode can not be properly read by a reading machine, even if it is visually readable. Then there has been a problem in the bar code readability.
On the other hand, thermosensitive recording media utilizing specific combinations of color developing agents and stabilizers to improve the preservation property of the image portion (References 1 and 2), and thermosensitive recording media utilizing specific combinations of sensitizers and stabilizers to improve the preservation property of the image portion (Reference 3) have been disclosed.
Further, thermosensitive recording media utilizing a combination of two specific color developing agents to improve the color developing property and the preservation property of the image portion (Reference 4) and thermosensitive recording media utilizing a combination of two specific color developing agents of urea-urethane-based compound and BPS based color developing agent to improve the preservation property (References 5 to 8) are disclosed.